Loudspeaker construction



'Nov. 15, 1966 COHEN 3,285,364

LOUDSPEAKER CONSTRUCTION Filed June 1, 1965 1 ABRAHAM B. COHEN 11 INVENTOR FIG I BY/4,,.,M%

AGENT United States Patent 3,285,364 LOUDSPEAKER CONSTRUCTION Abraham B. Cohen, Oklahoma City, Okla., assignor to Ling-Temco-Vought, Inc., Dallas, Tex., a corporation of Delaware Filed June 1, 1965, Ser. No. 460,241 6 Claims. (Cl. 181-31) This invention relates to speaker diaphragms and particularly to diaphragms that have lightweight stiff vibratile members molded directly to the surfaces of continuous compliant damping supporting members.

A speaker diaphragm according tothis invention is readily fabricated in a single molding operation. When the diaphragm is removed from a mold, it is complete except for cementing a voice coil to a mounting area that is formed by the molding operation. A lightweight stiff material is molded to a continuous sheet of compliant material to provide a desired backing and support for a main vibratile body or piston. The edge of the compliant material extends beyond the outer edge of the main vibratile body to provide the usual compliant support between the vibratile body and 'a speaker frame. A usual round opening through the vibratile body is provided at the point where a voice coil is to be attached. to the diaphragm. The compliant material may be porous and extend across this opening to provide a dust cover for the voice coil. The main body may be composed of a stiff cellular material such as polystyrene foam to provide good frequency response and still' prevent sectional vibrations.

An object of the present invention is to provide a speaker diaphragm that is completely formed in a single molding operation.

Another object is to provide a speaker diaphragm and speaker frame that are formed in a single operation.

Other objects and advantages will be apparent from the specification and claims and from the accompanying drawings in which:

FIG. 1 is a front view of a speaker diaphragm that has a continuous compliant backing;

FIG. 2 is a cross section of the speaker diaphragm of FIG. 1;

FIG. 3 is a front, oblique view of a speaker diaphragm and a frame or housing that are molded simultaneously; and

FIG. 4 is a cross section of the speaker and frame of FIG. 3.

In FIG. 1, a speaker diaphragm, which may have a conventional conical slope as shown or have a pyramidal shape, etc., comprises a compliant backing 12 to which is molded a stiff vibratile portion 13. The vibratile portion extends from the outer edge of the cone to an area 14 to which a voice coil is to be mounted. The vibratile portion 13 can be molded from lightweight stiff paper pulp products or from plastic molding materials of either thermosetting or thermoplastic types. A preferred material is polystyrene foam. The compliant material 12 may also be molded from suitable paper pulp products or from plastics. A preferred material is polyurethane foam.

To fabricate a diaphragm of preferred materials, a sheet of polyurethane foam is positioned in a mold. As is taught at page 295 of Modern Plastics Encyclopedia 1965, volume 42 Ho. 1A (September 1964), flexible (hence, compliant) foamed polyurethane plastics are open-celled. Expandable polystyrene in the form of beads is passed through a steam chamber to start its expansion and is forced into the enclosed mold under pressure. The polystyrene beads continue to expand in the mold. until the cavity for forming the vibratile portion 13 is completely filled. The beads weld together and also fill the pores or cells on that portion of the exposed surface of the polyurethane sheet that is enclosed by the cavity so that the polystyrene adheres firmly to the polyurethane.

When the diaphragm is removed from the mold, it is ready to have a voice coil mounted in place about the area 14 in the polystyrene foam. The ring of polyurethane that extends beyond the outer edge of the polystyrene foam is attached to the speaker frame or basket and supplies the required stiffness in conjunction with the mass of the polystyrene vibratile portion as required for resonance at a low audio frequency. When the compliant material is porous, the section of the compliant material covering the area 14 can remain over the voice coil as a dust cover.

A molded unit that comprises both diaphragm and speaker frame is shown in FIGS. 3 and 4. The diaphragm is similar to that shown in FIGS. 1 and. 2. Stiff cellular material 15, for example, polystyrene foam, is molded to compliant material 16, for example, polyurethane foam, to form the vibratile body or piston. While the diaphragm is being molded, lightweight stiff material for forming a frame 17 is simultaneously injected into a cavity of the mold that extends perpendicularly from the outer edge of the compliant sheet 16. The material that is being injected into the cavity for the frame penetrates into the pores of the compliant material 15 to provide a strong bond between them. Both the vibrating body 15 and the frame 17 may be molded from polystyrene, or each may be molded from any suitable paper pulp product or from suitable plastic materials.

Speaker diaphragms according to this invention are quickly produced in large number. The compliant sheet that extends over the full area of each diaphragm provides a ready support for the edge of the vibratile body and. a dust cover for a voice coil. In addition, the compliant material serves as a compliant backing which damps and breaks up zonal and sectoral vibrations of the diaphragm. In addition by molding a frame on the edge of the compliant sheet, the diaphragm is secured to the frame without having to resort to a cementing operation. A magnetic structure for a voice coil can be fastened to the frame 17 by suitable clamping means. A relatively thin speaker can be fabricated by this molding method for placement within the wall structure of a listening area. For example, a speaker of this type can be suitably located within the space between the fabric headliner and roof of an automobile so that sound from the speaker is quite evenly distributed to passengers in different seating positions within the automobile.

While only two embodiments of the invention, together with modifications thereof, have been described in detail herein and shown in the accompanying drawing, it will be evident that various further modifications are possible in the arrangement and construction of its components without departing from the scope of the invention.

I claim:

1. A unitary molded loudspeaker diaphragm comprising a shaped continuous sheet of compliant, open-celled, foamed plastic material and a vibratile surface portion molded thereon, said sheet having a peripheral mounting area free from coverage by said vibratile surface portion and said diaphragm being adapted to be mounted within a speaker mounting frame by having the periphery of said sheet secured to said frame, said vibratile surface portion having a portion adapted for mounting a voice coil and having a face substantially completely covered by said compliant, foamed plastic material, said vibratile surface portion being lightweight, stiff, closed-celled,

foamed plastic material that is molded in situ onto surface portions of said sheet of compliant, foamed plastic material intermediate its peripheral mounting area and said portion adapted for mounting a voice coil to cause mechanical interlocking of material of said vibratile portion with cells of said com-pliant material, whereby said sheet of compliant material serves to damp undesired vibrations arising in and provides means for compliant support of said vibratile surface portion.

2. A loudspeaker diaphragm as claimed in claim 1 wherein said compliant plastic material is polyurethane foam sheet.

3. A loudspeaker diaphragm as claimed in claim 1 in which said vibratile surface portion is polystyrene foam.

4. A unitary molded loudspeaker structure comprising:

a peripheral frame of lightweight stiff cellular material and having an edge,

a diaphragm comprising a continuous sheet of compliant, open-celled, foamed plastic material having a peripheral area and a vibratile portion of lightweight, stiff, foamed plastic material contiguous with said peripheral area and spaced from said frame, a portion of the peripheral area of said compliant, opencelled, foamed plastic material being molded within the edge of said frame to cause said cellular material of the frame to interlock with the open cells of the compliant plastic material, and said compliant plastic material being formed so as to be positioned within said frame, said vibratile portion of lightweight, stiff, foamed plastic material having a portion adapted for mounting a voice coil,

said vibratile portion of lightweight, stiff, closed-celled, foamed plastic material being molded in situ onto said compliant, open-celled, foamed plastic material to cause material of said vibratile portion to mechanically interlock With cells of said compliant, opencelled material, said compliant plastic material forming a mechanically resistive surface over substantially all of said vibratile portion of lightweight, stiff, foamed plastic material to prevent localized breakup of said diaphragm and further forming compliant means mounting said diaphragm in said frame. 5. A molded loudspeaker structure as claimed in claim 4 in which said frame and said vibratile portion of lightweight, stiff, foamed plastic material are polystyrene foam. 6. A molded loudspeaker structure as claimed in claim 4 in which said compliant plastic material is polyurethane foam sheet.

References Cited by the Examiner UNITED STATES PATENTS 2,881,850 4/1959 Bonn 18131 2,905,260 9/ 1959 Williams 18132 3,046,362 7/1962 White 181--32 X 3,093,207 6/1963 Bozak 181--32 FOREIGN PATENTS 736,247 6/ 1943 Germany.

513,289 10/ 1939 Great Britain.

625,014 6/ 1949 Great Britain.

RICHARD B. WILKINSON, Primary Examiner.

LOUIS J. CAPOZI, Examiner.

S. I. TOMSKY, Assistant Examiner. 

1. A UNITARY MOLDED LOUDSPEAKER DIAPHRAGM COMPRISING A SHAPED CONTINUOUS SHEET OF COMPLIANT, OPEN-CELLED, FOAMED PLASTIC MATERIAL AND A VIBRATILE SURFACE PORTION MOLDED THEREON, SAID SHEET HAVING A PERIPHERAL MOUNTING AREA FREE FROM COVERAGE BY SAID VIBRATILE SURFACE PORTION AND SAID DIAPHRAGM BEING ADAPTED TO BE MOUNTED WITHIN A SPEAKER MOUNTING FRAME BY HAVING THE PERIPHERY OF SAID SHEET SECURED TO SAID FRAME, SAID VIBRATILE SURFACE PORTION HAVING A PORTION ADAPTED FOR MOUNTING A VOICE COIL AND HAVING A FACE SUBSTANTIALLY COMPLETELY COVERED BY SAID COMPLIANT, FOAMED PLASTIC MATERIAL, SAID VIBRATILE SURFACE PORTION BEING LIGHWEIGHT, STIFF, CLOSED-CELLED, FOAMED PLASTIC MATERIAL THAT IS MOLDED IN SITU ONTO SURFACE PORTIONS OF SAID SHEET OF COMPLIANT, FOAMED PLASTIC MATERIAL INTERMEDIATE ITS PERIPHERAL MOUNTING AREA AND SAID PORTION ADAPTED FOR MOUNTING A VOICE COIL TO CAUSE MECHANICAL INTERLOCKING OF MATERIAL OF SAID VIBRATILE PORTION WITH CELLS OF SAID COMPLIANT MATERIAL, WHEREBY SAID SHEET OF COMPLIANT MATERIAL SERVES TO DAMP UNDESIRED VIBRATIONS ARISING IN AND PROVIDES MEANS FOR COMPLIANT SUPPORT OF SAID VIBRATILE SURFACE PORTION. 